Radiation image reading device

ABSTRACT

A radiation image reading device includes: a light scanning unit; a light detection unit. Each of a transmittance when the excitation light reflected from the surface of the recording medium is transmitted through the optical filter and a transmittance when the signal light emitted from the surface of the recording medium at an angle larger than a predetermined angle with respect to a direction perpendicular to the scan line within the detection surface is transmitted through the optical filter is smaller than a transmittance when the signal light emitted from the surface of the recording medium at an angle smaller than the predetermined angle with respect to a direction perpendicular to the scan line within the detection surface is transmitted through the optical filter.

TECHNICAL FIELD

An aspect of the present invention relates to a radiation image readingdevice.

BACKGROUND ART

A radiation image reading device including a light scanning unit whichscans excitation light onto a surface of a recording medium having aradiation image recorded thereon and a light detection unit whichdetects signal light emitted from the surface of the recording medium bythe scanning of the excitation light is known (for example, see PatentLiterature 1).

CITATION LIST Patent Literature

Patent Literature 1: Japanese Unexamined Patent Publication No.2002-77548

SUMMARY OF INVENTION Technical Problem

In the above-described radiation image reading device, a decrease indevice size may be required in some cases. However, for example, whenthe light detection unit is disposed so that a distance from the surfaceof the recording medium decreases in order to realize a decrease indevice size, there is a possibility that radiation image detectionaccuracy decreases.

Therefore, an object of an aspect of the invention is to provide aradiation image reading device capable of decreasing a device size andmaintaining radiation image detection accuracy.

Solution to Problem

A radiation image reading device according to an aspect of the inventionincludes: a light scanning unit which scans excitation light to asurface of a recording medium having a radiation image recorded thereonalong a scan line; a light detection unit which detects signal lightemitted from the surface of the recording medium by the scanning of theexcitation light within a detection surface intersecting the surface ofthe recording medium and including the scan line; and an optical filterwhich is disposed between the light detection unit and the surface ofthe recording medium, in which each of a transmittance when theexcitation light reflected from the surface of the recording medium istransmitted through the optical filter and a transmittance when thesignal light emitted from the surface of the recording medium at anangle larger than a predetermined angle with respect to a directionperpendicular to the scan line within the detection surface istransmitted through the optical filter is smaller than a transmittancewhen the signal light emitted from the surface of the recording mediumat an angle smaller than the predetermined angle with respect to adirection perpendicular to the scan line within the detection surface istransmitted through the optical filter.

In the radiation image reading device, each of the transmittance whenthe excitation light reflected from the surface of the recording mediumis transmitted through the optical filter and the transmittance when thesignal light emitted from the surface of the recording medium at anangle larger than the predetermined angle is transmitted through theoptical filter is smaller than the transmittance when the signal lightemitted from the surface of the recording medium at an angle smallerthan the predetermined angle is transmitted through the optical filter.Accordingly, it is possible to suppress a decrease in radiation imagedetection accuracy since the excitation light is incident to the lightdetection unit. Further, even when the light detection unit is disposedso that a distance from the surface of the recording medium decreasesand the length of the light detection unit in a direction parallel tothe scan line is limited in order to realize a decrease in device size,it is possible to suppress a decrease in radiation image detectionaccuracy since the signal light has a diverging angle. The reason whythe radiation image detection accuracy decreases since the signal lighthas a diverging angle is as below. That is, since the signal lightemitted from the surface of the recording medium has a diverging angle,when the light detection unit is disposed so that a distance from thesurface of the recording medium decreases and the length of the lightdetection unit in a direction parallel to the scan line is limited inorder to decrease the device size, for example, the entire signal lightis incident to the light detection unit at the center portion of thescan line and the entire signal light is not incident to the lightdetection unit at both end portions of the scan line. That is, in theradiation image reading device, it is possible to suppress a differencein detection range of the signal light emitted from the surface of therecording medium at the center portion and both end portions of the scanline even when the device size decreases. As described above, accordingto the radiation image reading device, it is possible to decrease adevice size and to maintain the radiation image detection accuracy.

In the radiation image reading device according to an aspect of theinvention, when a scan region of the excitation light and a detectionregion of the signal light have a centering alignment relationshipwithin the detection surface, an equation of θ=tan−1 {(W2−W1)/2D} may beestablished on the assumption that a width of the scan region isindicated by W1, a width of the detection region is indicated by W2(>W1), a distance between the scan region and the detection region isindicated by D, and the predetermined angle is indicated by θ. Accordingto this configuration, since the detection range of the signal lightemitted from the surface of the recording medium is the same at thecenter portion and both end portions of the scan line, it is possible tomore reliably suppress a decrease in radiation image detection accuracy.

In the radiation image reading device according to an aspect of theinvention, the optical filter may include a glass plate, a firstdielectric multilayer film formed on one surface of the glass plate, anda second dielectric multilayer film formed on the other surface of theglass plate, and each of a transmittance when the excitation lightreflected from the surface of the recording medium is transmittedthrough the first dielectric multilayer film and the second dielectricmultilayer film and a transmittance when the signal light emitted fromthe surface of the recording medium at an angle larger than thepredetermined angle with respect to a direction perpendicular to thescan line within the detection surface is transmitted through the firstdielectric multilayer film and the second dielectric multilayer film maybe smaller than a transmittance when the signal light emitted from thesurface of the recording medium at an angle smaller than thepredetermined angle with respect to a direction perpendicular to thescan line within the detection surface is transmitted through the firstdielectric multilayer film and the second dielectric multilayer film.According to this configuration, it is possible to easily and reliablyobtain the optical filter having the above-described function.

The radiation image reading device according to an aspect of theinvention may further include an optical element which is disposedbetween the surface of the recording medium and the optical filter andhas a function of converges the excitation light reflected from thesurface of the recording medium and the signal light emitted from thesurface of the recording medium only within a surface perpendicular tothe detection surface. According to this configuration, one includingthe plurality of photodetector elements arranged along a directionparallel to the scan line can be used as the light detection unit.

In the radiation image reading device according to an aspect of theinvention, the light detection unit may include a plurality ofphotodetector elements arranged along a direction parallel to the scanline and the plurality of photodetector elements may be controlled asone channel. According to this configuration, it is possible to read theradiation image with a simpler configuration.

Advantageous Effects of Invention

According to an aspect of the invention, it is possible to provide aradiation image reading device capable of decreasing a device size andmaintaining radiation image detection accuracy.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a configuration diagram of a radiation image reading device ofan embodiment and is a diagram at the time of reading a radiation image.

FIG. 2 is a perspective view of a part of the radiation image readingdevice of FIG. 1.

FIG. 3 is a configuration diagram of a light detection unit of theradiation image reading device of FIG. 1.

FIG. 4 is a configuration diagram of an optical filter of the radiationimage reading device of FIG. 1.

FIG. 5 is a diagram illustrating a transmittance characteristic withrespect to an embodiment of an optical filter of FIG. 4.

FIG. 6 is an enlarged view of a part of the radiation image readingdevice of FIG. 1.

FIG. 7 is a configuration diagram of the radiation image reading deviceof FIG. 1 and is a diagram at the time of erasing a radiation image.

FIG. 8 is a cross-sectional view taken along a line VIII-VIII of FIG. 6.

FIG. 9 is a diagram illustrating a light intensity distribution withrespect to an excitation light scan position.

FIG. 10(a) is a configuration diagram of an optical filter of a firstmodified example, FIG. 10(b) is a configuration diagram of an opticalfilter of a second modified example, and FIG. 10(c) is a configurationdiagram of an optical filter of a third modified example.

DESCRIPTION OF EMBODIMENTS

Hereinafter, an embodiment of the invention will be described in detailwith reference to the drawings. Furthermore, the same reference numeralswill be given to the same or corresponding parts of the drawings and arepetitive description thereof will be omitted.

As illustrated in FIG. 1, a radiation image reading device 1 includes acasing 2, a plurality of conveying roller pairs 3, a carry-in detectionsensor 4, a light scanning unit 5, an optical element 6, an opticalfilter 10, a light detection unit 7, and a radiation image erasing unit8. The radiation image reading device 1 is a device which reads aradiation image recorded on an imaging plate (a recording medium) IP.

The casing 2 accommodates the plurality of conveying roller pairs 3, thecarry-in detection sensor 4, the light scanning unit 5, the opticalelement 6, the optical filter 10, the light detection unit 7, and theradiation image erasing unit 8. The casing 2 protects componentsaccommodated in the casing 2 from the outside and shields light from theoutside. The casing 2 is provided with an inlet 2 a into which theimaging plate IP is conveyed and an outlet 2 b from which the imagingplate IP is conveyed. The inlet 2 a is provided in one wall portion ofthe casing 2 in the X-axis direction. The outlet 2 b is provided in theother wall portion of the casing 2 in the X-axis direction.

The plurality of conveying roller pairs 3 are arranged along parallel inthe X-axis direction to be separated from each other. A pair of rollers31 constituting each conveying roller pair 3 extends along the Y-axisdirection and faces each other in the Z-axis direction while beingseparated from each other. A gap between the pair of rollers 31 issubstantially the same as the thickness of the imaging plate IP. Theplurality of conveying roller pairs 3 are disposed so that the positionof the gap between the pair of rollers 31 is substantially the same asthe positions of the inlet 2 a and the outlet 2 b in the Z-axisdirection. In the radiation image reading device 1, the imaging plate IPis conveyed from the inlet 2 a, is conveyed along the X-axis directionby the plurality of conveying roller pairs 3, and is conveyed from theoutlet 2 b.

The carry-in detection sensor 4 is disposed in the vicinity of the inlet2 a of the casing 2. The carry-in detection sensor 4 detects whether theimaging plate IP is carried in when the imaging plate IP is carried infrom the inlet 2 a. As the carry-in detection sensor 4, for example, amechanical switch (for example, Omron D2F-01FL-D3) may be used or aphotodetector type sensor such as a photo interrupter may be used.Furthermore, it is desirable to use a mechanical switch when consideringconcern that the radiation image recorded on the imaging plate IP may bedeteriorated due to the irradiation of the light emitted from thephotodetector type sensor.

As illustrated in FIGS. 1 and 2, the light scanning unit 5 includes anexcitation light source unit 51 and a position adjustment mirror 52. Theexcitation light source unit 51 includes an excitation light source (notillustrated) and a micro electro mechanical system (MEMS) mirror (notillustrated). The excitation light source unit 51 emits excitation lightEL along the X-axis direction while swinging the excitation light ELabout an axis parallel to the Z-axis direction. The position adjustmentmirror 52 is configured to adjust the direction of a reflection surfaceabout an axis parallel to the Y-axis direction. The position adjustmentmirror 52 reflects the excitation light EL emitted from the excitationlight source unit 51 to a scan line L. The scan line L is an imaginaryline located on a surface IPa of the imaging plate IP (a surfacerecording the radiation image) conveyed by the plurality of conveyingroller pairs 3 and is, for example, a line parallel to the Y-axisdirection. In the radiation image reading device 1, the light scanningunit 5 scans the excitation light EL along the scan line L with respectto the surface IPa of the imaging plate IP recording the radiation image(that is, the irradiation region (the light collection region) of theexcitation light EL is moved along the scan line L in a reciprocatingmanner).

The light detection unit 7 is disposed to face the scan line L in theZ-axis direction. The light detection unit 7 detects signal light FLemitted from the surface IPa of the imaging plate IP by the scanning ofthe excitation light EL within the detection surface S. The detectionsurface S is an imaginary plane which includes the scan line L andintersects the surface IPa of the imaging plate IP and is, for example,a surface which is parallel to the YZ plane.

As illustrated in FIG. 3, the light detection unit 7 includes aplurality of photo diodes (photodetector elements) 71, a switch 72, anamplifier 73, and an A/D converter 74. The light detection unit 7 is,specifically, a MPPC (multi-pixel photon counter). The MPPC is a photoncounting device which includes pixels of the plurality of photo diodes71. The plurality of photo diodes 71 are arranged along the Y-axisdirection (that is, a direction parallel to the scan line L). Theplurality of photo diodes 71 are connected in parallel to one end of oneswitch 72 through a wire 75. The amplifier 73 is connected to the otherend of the switch 72. The A/D converter 74 is connected to the amplifier73. Furthermore, potentials having different polarities are applied tothe photo diode 71. Among them, one potential V2 may be referred to as aground potential.

When the signal light FL is incident to the light detection unit 7, eachphoto diode 71 outputs an electric signal in response to the lightamount of the incident signal light FL. The electric signals output fromthe photo diodes 71 are added and are output to, for example, a controlunit (not illustrated) through the amplifier 73 and the A/D converter74. That is, the plurality of photo diodes 71 are controlled as onechannel.

As illustrated in FIGS. 1 and 2, the optical filter 10 is disposedbetween the scan line L and the light detection unit 7. That is, theoptical filter 10 is disposed between the light detection unit 7 and thesurface IPa of the imaging plate IP conveyed by the plurality ofconveying roller pairs 3. The optical filter 10 attenuates theexcitation light EL reflected from the surface IPa of the imaging plateIP. Further, the optical filter 10 attenuates the signal light FLemitted from the surface IPa of the imaging plate IP at an angle largerthan a predetermined angle with respect to a direction perpendicular tothe scan line L within the detection surface S and transmits the signallight FL emitted from the surface IPa of the imaging plate IP at anangle smaller than the predetermined angle with respect to a directionperpendicular to the scan line L within the detection surface S.

Furthermore, the optical filter 10 transmits the signal light FL emittedfrom the surface IPa of the imaging plate IP at a predetermined anglewith respect to a direction perpendicular to the scan line L within thedetection surface S.

Here, the “case of attenuating the excitation light EL reflected fromthe surface IPa of the imaging plate IP” means a case in which thetransmittance when the excitation light EL is transmitted through theoptical filter 10 is less than 50% on average. The “case of attenuatingthe signal light FL emitted from the surface IPa of the imaging plate IPat an angle larger than the predetermined angle with respect to adirection perpendicular to the scan line L within the detection surfaceS” means a case in which the transmittance when the signal light FL istransmitted through the optical filter 10 is less than 50% on average.The “case of transmitting the signal light FL emitted from the surfaceIPa of the imaging plate IP at an angle smaller than the predeterminedangle with respect to a direction perpendicular to the scan line Lwithin the detection surface S” means a case in which the transmittancewhen the signal light FL is transmitted through the optical filter 10 is50% or more on average.

As illustrated in FIG. 4, the optical filter 10 includes a glass plate11, a first dielectric multilayer film 12, and a second dielectricmultilayer film 13. The glass plate 11 includes a first surface (onesurface) 11 a and a second surface (the other surface) 11 b which faceeach other in the Z-axis direction. The first surface 11 a is a surfaceon the side of the scan line L in the glass plate 11. The second surface11 b is a surface on the side of the light detection unit 7 in the glassplate 11. The glass plate 11 is a member that allows the signal light FLto be transmitted therethrough. The glass plate 11 is formed as a colorglass having a property of absorbing the excitation light EL. The firstdielectric multilayer film 12 is formed on the first surface 11 a. Thesecond dielectric multilayer film 13 is formed on the second surface 11b. Each of the first dielectric multilayer film 12 and the seconddielectric multilayer film 13 is, for example, a lamination structureformed by alternately laminating S102 and Ta2O5. The first dielectricmultilayer film 12 and the second dielectric multilayer film 13 arerespectively formed on the first surface 11 a and the second surface 11b of the glass plate 11 by, for example, sputtering or vapor-depositing.

In the optical filter 10, the first dielectric multilayer film 12 andthe second dielectric multilayer film 13 attenuate the excitation lightEL reflected from the surface IPa of the imaging plate IP conveyed bythe plurality of conveying roller pairs 3 and the signal light FLemitted from the surface IPa of the imaging plate IP at an angle largerthan the predetermined angle with respect to a direction perpendicularto the scan line L within the detection surface S and allows the signallight FL emitted from the surface IPa of the imaging plate IP to betransmitted at an angle smaller than the predetermined angle withrespect to a direction perpendicular to the scan line L within thedetection surface S.

FIG. 5 is a diagram illustrating a transmittance characteristic of anembodiment of the optical filter 10. The inventors have investigated thetransmittance of the light when light of various wavelengths is incidentto the optical filter 10 at an angle (here, referred to as an “incidentangle”) with respect to a direction perpendicular to the scan line Lwithin the detection surface S in an embodiment of the optical filter10. As illustrated in FIG. 5, the transmittance is substantially 0regardless of the incident angle at the wavelength of 650 nmcorresponding to the wavelength of the excitation light EL. Further, atthe wavelength of 400 nm corresponding to the wavelength of the signallight FL, the transmittance was higher than 95% at the incident angle of0°, 20°, and 40° and the transmittance was lower than 20% at theincident angle of 60°. That is, according to an embodiment of theoptical filter 10, it was found that an angle larger than 40° andsmaller than 60° can be set to the above-described predetermined anglewhen the wavelength of the signal light FL is 400 nm.

As illustrated in FIGS. 1 and 2, the optical element 6 is disposedbetween the scan line L and the optical filter 10. That is, the opticalelement 6 is disposed between the optical filter 10 and the surface IPaof the imaging plate IP conveyed by the plurality of conveying rollerpairs 3.

As illustrated in FIG. 6, the optical element 6 is, for example, a rodlens having a columnar shape of which an axis parallel to the Y-axisdirection is set as a center axis. Accordingly, the optical element 6converges the excitation light EL and the signal light FL incident tothe optical element 6 onto a line where the plurality of photo diodes 71are arranged within a plane parallel to the ZX plane. On the other hand,the optical element 6 allows the excitation light EL and the signallight FL incident to the optical element 6 to be incident to theplurality of photo diodes 71 while not substantially converging thoselights within the detection surface S. That is, the optical element 6has a function of converging the excitation light EL reflected from thesurface IPa of the imaging plate IP and the signal light FL emitted fromthe surface IPa of the imaging plate IP only within a surface (that is,a surface parallel to the ZX plane) perpendicular to the detectionsurface S.

As illustrated in FIGS. 1 and 2, the radiation image erasing unit 8 isdisposed on the downstream side of the scan line L in the conveyingdirection of the imaging plate IP. The radiation image erasing unit 8erases the radiation image from the surface IPa of the imaging plate IP,for example, by irradiating white light to the surface IPa of theimaging plate IP. As the radiation image erasing unit 8, for example, awhite lamp such as a white LED (light emitting diode), a fluorescentlamp, or the like is used.

In the radiation image reading device 1 with the above-describedconfiguration, the radiation image recorded on the imaging plate IP isread as below.

As illustrated in FIG. 1, the imaging plate IP is carried in from theinlet 2 a into the casing 2 while the surface IPa of the imaging plateIP faces the light detection unit 7. At this time, the carried in of theimaging plate IP is detected by the carry-in detection sensor 4 and theoperations of the conveying roller pair 3 and the light scanning unit 5are started. The imaging plate IP which is conveyed into the casing 2 isconveyed by the conveying roller pair 3 along the X-axis direction. Whenthe imaging plate IP is conveyed to a position facing the lightdetection unit 7, the light scanning unit 5 scans the excitation lightEL along the scan line L with respect to the surface IPa of the imagingplate IP. The excitation light EL scanning the surface IPa of theimaging plate IP is reflected from the surface IPa of the imaging plateIP. At the same time, the signal light FL is emitted from the surfaceIPa of the imaging plate IP scanned by the excitation light EL. Thelight detection unit 7 detects the signal light FL transmitted throughthe optical element 6 and the optical filter 10. Then, as illustrated inFIG. 7, the imaging plate IP is conveyed out from the outlet 2 b afterthe radiation image recorded on the surface IPa of the imaging plate IPis erased by the radiation image erasing unit 8. According to theradiation image reading device 1, it is possible to form the radiationimage by irradiating the excitation light EL to the entire region wherethe radiation image is recorded on the surface IPa of the imaging plateIP and detecting the signal light FL in the entire region.

Next, a relationship between the scan region of the excitation light ELand the detection region of the signal light FL will be described.

As illustrated in FIG. 8, the width of the scan region R1 of theexcitation light EL (the width in the Y-axis direction) within thedetection surface S is W1. The scan region R1 of the excitation light ELmeans a range in which the surface IPa of the imaging plate IP isscanned by the excitation light EL within the detection surface S. Thatis, the width W1 of the scan region R1 of the excitation light EL is thesame as the length of the scan line L within the detection surface S.The width of the detection region R2 of the signal light FL (the widthin the Y-axis direction) within the detection surface S is W2. Thedetection region R2 of the signal light FL means a range in which lightis detected by the light detection unit 7 within the detection surfaceS. That is, the same in the plurality of photo diodes 71 arranged alongthe Y-axis direction. The width W2 of the detection region R2 of thesignal light FL is longer than the width W1 of the scan region R1 of theexcitation light EL within the detection surface S. The scan region R1of the excitation light EL and the detection region R2 of the signallight FL have a centering alignment relationship within the detectionsurface S. The centering alignment relationship means a state in whichthe center position of the scan region R1 of the excitation light EL(the center position in the Y-axis direction) and the center position ofthe detection region R2 of the signal light FL (the center position inthe Y-axis direction) are aligned to each other in the Y-axis directionwithin the detection surface S. The distance between the scan region R1of the excitation light EL and the detection region R2 of the signallight FL in the Z-axis direction is D. At this time, when thepredetermined angle for the optical filter 10 is θ, an equation ofθ=tan−1 {(W2−W1)/2D} is established.

As described above, in the radiation image reading device 1, theexcitation light EL reflected from the surface IPa of the imaging plateIP is attenuated by the optical filter 10. That is, the excitation lightEL reflected from the surface IPa of the imaging plate IP at an anglesmaller than the predetermined angle θ with respect to a directionperpendicular to the scan line L within the detection surface S, theexcitation light EL reflected from the surface IPa of the imaging plateIP at an angle larger than the predetermined angle θ with respect to adirection perpendicular to the scan line L within the detection surfaceS, and the excitation light EL reflected from the surface IPa of theimaging plate IP at the predetermined angle θ with respect to adirection perpendicular to the scan line L within the detection surfaceS are attenuated by the optical filter 10. Accordingly, it is possibleto suppress a decrease in radiation image detection accuracy since theexcitation light EL is incident to the light detection unit 7. Further,in the radiation image reading device 1, the signal light FL emittedfrom the surface IPa of the imaging plate IP at an angle larger than thepredetermined angle θ is attenuated by the optical filter 10 and thesignal light FL emitted from the surface IPa of the imaging plate IP atan angle smaller than the predetermined angle θ is transmitted throughthe optical filter 10. Accordingly, even when the light detection unit 7is disposed so that a distance from the surface IPa of the imaging plateIP decreases and the length of the light detection unit 7 in a directionparallel to the scan line L is limited in order to decrease the devicesize, it is possible to suppress a decrease in radiation image detectionaccuracy since the signal light FL has a diverging angle. As describedabove, according to the radiation image reading device 1, it is possibleto decrease the device size and to maintain the radiation imagedetection accuracy.

The reason why the radiation image detection accuracy decreases due tothe diverging angle of the signal light FL is as below. That is, sincethe signal light FL emitted from the surface IPa of the imaging plate IPhas the diverging angle, when the light detection unit 7 is disposed sothat a distance from the surface IPa of the imaging plate IP decreasesand the length of the light detection unit 7 in a direction parallel tothe scan line L is limited in order to realize a decrease in devicesize, for example, the entire signal light is incident to the lightdetection unit 7 at the center portion of the scan line L and the entiresignal light FL is not incident to the light detection unit 7 at bothend portions of the scan line L (both end portions of the scan region R1of the excitation light EL).

Specifically, as illustrated in FIG. 8, signal light FL1 travelingtoward the other end portion of the scan line L with respect to adirection perpendicular to the scan line L between the signal lightFL2(FL) emitted from the surface IPa of the imaging plate IP at an anglesmaller than the predetermined angle θ with respect to a directionperpendicular to the scan line L and the signal light FL1 (FL) emittedfrom the surface IPa of the imaging plate IP at an angle larger than thepredetermined angle θ with respect to a direction perpendicular to thescan line L, for example, at one end portion of the scan line L withinthe detection surface S is incident to the light detection unit 7. Onthe other hand, the signal light FL1 traveling toward the opposite sideto the other end portion of the scan line L with respect to a directionperpendicular to the scan line L in the signal light FL1(FL) emittedfrom the surface IPa of the imaging plate IP at an angle larger than thepredetermined angle θ with respect to a direction perpendicular to thescan line L is not incident to the light detection unit 7. As describedabove, a difference in detection range of the signal light FL emittedfrom the surface IPa of the imaging plate IP is generated at the centerportion and both end portions of the scan line L.

As described above, in the radiation image reading device 1, the opticalfilter 10 attenuates the signal light FL1 (FL) emitted from the surfaceIPa of the imaging plate IP at an angle larger than the predeterminedangle θ with respect to a direction perpendicular to the scan line L.That is, in the radiation image reading device 1, it is possible tosuppress a difference in detection range of the signal light FL emittedfrom the surface IPa of the imaging plate IP at the center portion andboth end portions of the scan line L even when the device sizedecreases.

In a conventional radiation image reading device, there is a case inwhich the dielectric multilayer film that attenuates the excitationlight EL reflected from the surface IPa of the imaging plate IP along adirection perpendicular to the scan line L within the detection surfaceS is employed as an excitation light cut filter. In such a case, theexcitation light EL reflected from the surface IPa of the imaging plateIP at a predetermined angle with respect to a direction perpendicular tothe scan line L within the detection surface S is not sufficientlyattenuated. FIG. 9 is a diagram illustrating a light intensitydistribution detected by the photo diode 71 disposed at the center ofthe light detection unit 7 in the Y-axis direction when such anexcitation light cut filter is employed. Furthermore, FIG. 9 illustratesa light intensity distribution when the excitation light EL is scannedalong the scan line L a plurality of times and a dashed line correspondsto a position facing the photo diode 71 disposed at the center (the scanposition of the excitation light EL). In this case, the excitation lightEL reflected from the surface IPa of the imaging plate IP at apredetermined angle with respect to a direction perpendicular to thescan line L within the detection surface S is incident to the lightdetection unit 7. For this reason, as illustrated in FIG. 9, the lightintensity distribution detected by the photo diode 71 disposed at thecenter of the light detection unit 7 in the Y-axis direction increasesat both sides in which the scan position of the excitation light EL isseparated from the dashed line. In contrast, in the radiation imagereading device 1, the optical filter 10 attenuates not only theexcitation light EL reflected from the surface IPa of the imaging plateIP with respect to a direction perpendicular to the scan line L withinthe detection surface S but also the excitation light EL reflected fromthe surface IPa of the imaging plate IP at a predetermined angle withrespect to a direction perpendicular to the scan line L within thedetection surface S. Accordingly, it is possible to suppress an increasein light intensity distribution detected by the photo diode 71 disposedat the center of the light detection unit 7 in the Y-axis direction atboth sides in which the scan position of the excitation light EL isseparated from the dashed line.

Further, in the radiation image reading device 1, when the scan regionR1 of the excitation light EL and the detection region R2 of the signallight FL have a centering alignment relationship within the detectionsurface S, an equation of θ=tan−1 {(W2−W1)/2D} is established on theassumption that the width of the scan region R1 is indicated by W1, thewidth of the detection region R2 is indicated by W2 (>W1), the distancebetween the scan region R1 and the detection region R2 is indicated byD, and the predetermined angle is indicated by θ. According to thisconfiguration, since the detection range of the signal light FL emittedfrom the surface IPa of the imaging plate IP is the same at the centerportion and both end portions of the scan line L, it is possible to morereliably suppress a decrease in radiation image detection accuracy.

Further, in the radiation image reading device 1, the optical filter 10includes the glass plate 11, the first dielectric multilayer film 12formed on the first surface 11 a of the glass plate 11, and the seconddielectric multilayer film 13 formed on the second surface 11 b of theglass plate 11. According to this configuration, it is possible toeasily and reliably obtain the optical filter 10 having theabove-described function. For example, when the first dielectricmultilayer film 12 and the second dielectric multilayer film 13 areformed as below, the optical filter 10 has the above-described function.That is, the first dielectric multilayer film 12 may attenuate thesignal light FL1(FL) emitted from the surface IPa of the imaging plateIP at an angle larger than the predetermined angle θ with respect to thescan line L within the detection surface S and the excitation light ELreflected from the surface IPa of the imaging plate IP at an anglesmaller than the predetermined angle θ with respect to the scan line Lwithin the detection surface S and the second dielectric multilayer film13 may attenuate the excitation light EL reflected from the surface IPaof the imaging plate IP at an angle larger than the predetermined angleθ with respect to the scan line L within the detection surface S. Inthis way, in the dielectric multilayer film according to an aspect, theoptical filter 10 having the above-described function can be obtained bycombining two kinds or more of dielectric multilayer films when it isdifficult to obtain the optical filter 10 having the above-describedfunction. Furthermore, the functions of the first dielectric multilayerfilm 12 and the second dielectric multilayer film 13 are not limited tothe above-described functions and the type of light to be attenuated byeach of the first dielectric multilayer film 12 and the seconddielectric multilayer film 13 can be arbitrarily set as long as theoptical filter 10 having the above-described function can be obtained.Further, since the glass plate 11 is formed as a color glass having aproperty of absorbing the excitation light EL, the excitation light ELreflected from the first dielectric multilayer film 12 and the seconddielectric multilayer film 13 inside the optical filter 10 is absorbedto the glass plate 11, it is possible to more reliably suppress aproblem in which the excitation light EL is incident to the lightdetection unit 7. Further, the first dielectric multilayer film 12 andthe second dielectric multilayer film 13 can be respectively stablyformed on the first surface 11 a and the second surface 11 b of theglass plate 11.

Further, in the radiation image reading device 1, the optical element 6having a function of converging the excitation light EL reflected fromthe surface IPa of the imaging plate IP and the signal light FL emittedfrom the surface IPa of the imaging plate IP only within a surfaceperpendicular to the detection surface S is disposed between the surfaceIPa of the imaging plate IP and the optical filter 10. According to thisconfiguration, one including the plurality of photo diodes 71 arrangedalong a direction parallel to the scan line L can be used as the lightdetection unit 7.

Further, in the radiation image reading device 1, the plurality of photodiodes 71 arranged along a direction parallel to the scan line L in thelight detection unit 7 are controlled as one channel. According to thisconfiguration, it is possible to read the radiation image with a simplerconfiguration.

Although embodiments of the invention have been described, an aspect ofthe invention is not limited to the above-described embodiments.

In the above-described embodiment, the plurality of photo diodes 71 ofthe light detection unit 7 are controlled as one channel, but theplurality of photo diodes 71 may be controlled as a plurality ofchannels. Since the plurality of photo diodes 71 are controlled as aplurality of channels, it is possible to reduce noise as compared with acase in which the plurality of photo diodes 71 are controlled as onechannel. Further, when the plurality of photo diodes 71 are controlledas a plurality of channels, even when the excitation light EL is notscanned along the scan line L, and the excitation light EL is scanned onthe entire scan region R1, the radiation image recorded on the surfaceIPa of the imaging plate IP can be read.

Further, in the above-described embodiment, the transmittance when the“excitation light EL reflected from the surface IPa of the imaging plateIP” is transmitted through the optical filter 10 is less than 50% onaverage, the transmittance when the “signal light FL emitted from thesurface IPa of the imaging plate IP at an angle larger than thepredetermined angle with respect to a direction perpendicular to thescan line L within the detection surface S” is transmitted through theoptical filter 10 is less than 50% on average, and the transmittancewhen the “signal light FL emitted from the surface IPa of the imagingplate IP at an angle smaller than the predetermined angle with respectto a direction perpendicular to the scan line L within the detectionsurface S” is transmitted through the optical filter 10 is 50% or moreon average, but the values of the transmittance are not limited thereto.If each of the transmittance (for example, the transmittance on average)when the “excitation light EL reflected from the surface IPa of theimaging plate IP” is transmitted through the optical filter 10 and thetransmittance (for example, the transmittance on average) when the“signal light FL emitted from the surface IPa of the imaging plate IP atan angle larger than the predetermined angle with respect to a directionperpendicular to the scan line L within the detection surface S” istransmitted through the optical filter 10 is smaller than thetransmittance (for example, the transmittance on average) when the“signal light FL emitted from the surface IPa of the imaging plate IP atan angle smaller than the predetermined angle with respect to adirection perpendicular to the scan line L within the detection surfaceS” is transmitted through the optical filter 10, it is possible todecrease the device size and to maintain the radiation image detectionaccuracy. Here, since the excitation light EL is generally stronger thanthe signal light FL, it is desirable that the transmittance when theexcitation light EL is transmitted through the optical filter 10 be lessthan 1% on average.

Further, in the above-described embodiment, the optical element 6 isformed in a columnar shape, but the shape of the optical element 6 doesnot matter as long as a function of converging the signal light FLemitted from the surface IPa of the imaging plate IP only within a planeperpendicular to the detection surface S is provided. Further, theoptical element 6, the optical filter 10, and the light detection unit 7may be in contact with one another (see FIG. 6) or may be separated fromone another.

Further, as illustrated in FIG. 10(a), both the first dielectricmultilayer film 12 and the second dielectric multilayer film 13 may beformed on the second surface 11 b of the glass plate 11. Specifically,the first dielectric multilayer film 12 may be formed on the secondsurface 11 b of the glass plate 11 and the second dielectric multilayerfilm 13 may be formed on the surface of the first dielectric multilayerfilm 12. Further, the second dielectric multilayer film 13 may be formedon the second surface 11 b of the glass plate 11 and the firstdielectric multilayer film 12 may be formed on the surface of the seconddielectric multilayer film 13.

Further, as illustrated in FIG. 10(b), the optical filter 10 may includea plurality of glass plates 11. In this case, the first dielectricmultilayer film 12 is formed on the surface 11 a of one glass plate 11and the second dielectric multilayer film 13 is formed on the surface 11b of the other glass plate 11. Then, the plurality of glass plates 11are connected to each other to be interposed by the first dielectricmultilayer film 12 and the second dielectric multilayer film 13.Further, as illustrated in FIG. 10(c), the first dielectric multilayerfilm 12 and the second dielectric multilayer film 13 may be connected toeach other to be interposed by the glass plate 11.

Further, in the above-described embodiment, the optical filter 10transmits the signal light FL emitted from the surface IPa of theimaging plate IP at the predetermined angle θ with respect to adirection perpendicular to the scan line L within the detection surfaceS, but the optical filter 10 may attenuate the signal light FL emittedfrom the surface IPa of the imaging plate IP at the predetermined angleθ with respect to a direction perpendicular to the scan line L withinthe detection surface S.

Further, in the above-described embodiment, an equation of θ=tan−1{(W2−W1)/2D} is established in the optical filter 10, but the size ofthe predetermined angle θ can be set as required as long as the opticalfilter 10 can attenuate the excitation light EL reflected from thesurface IPa of the imaging plate IP and the signal light FL1 (FL)emitted from the surface IPa of the imaging plate IP at an angle largerthan the predetermined angle θ with respect to a direction perpendicularto the scan line L within the detection surface S. Furthermore, adecrease in radiation image detection accuracy is suppressed as thepredetermined angle θ decreases.

Further, the predetermined angle θ can be recognized as below regardlesswhether the scan region R1 of the excitation light EL and the detectionregion R2 of the signal light FL have a centering alignment relationshipwithin the detection surface S. Referring to FIG. 8, the predeterminedangle θ can be recognized as an angle formed by an imaginary lineconnecting one end of the scan region R1 (one end in the Y-axisdirection) and one end of the detection region R2 (one end in the Y-axisdirection) with respect to a direction perpendicular to the scan line Lwithin the detection surface S. Alternatively, the predetermined angle θcan be recognized as an angle formed by an imaginary line connecting theother end of the scan region R1 (the other end in the Y-axis direction)and the other end of the detection region R2 (the other end in theY-axis direction) with respect to a direction perpendicular to the scanline L within the detection surface S. Furthermore, when the scan regionR1 of the excitation light EL and the detection region R2 of the signallight FL do not have a centering alignment relationship, thepredetermined angle θ is different at one side and the other side, butin that case, a small one between the predetermined angle θ at one sideand the predetermined angle θ at the other side is desirably employed asthe predetermined angle θ from the viewpoint of maintaining theradiation image detection accuracy.

Further, in the above-described embodiment, in the light detection unit7, the plurality of photo diodes 71 are arranged along one dimension inthe Y-axis direction, but the plurality of photo diodes 71 may bearranged in two dimensions within a plane parallel to the XY plane.

REFERENCE SIGNS LIST

1: radiation image reading device, 5: light scanning unit, 10: opticalfilter, 11: glass plate, 11 a: first surface, 11 b: second surface, 12:first dielectric multilayer film, 13: second dielectric multilayer film,6: optical element, 7: light detection unit, 71: photo diode(photodetector element), EL: excitation light, FL: signal light, IP:imaging plate (recording medium), IPa: surface of imaging plate, L: scanline, R1: scan region, R2: detection region, S: detection surface, W1:width of scan region, W2: width of detection region, D: distance betweenscan region and detection region, θ: predetermined angle.

1. A radiation image reading device comprising: a light scanning unitwhich scans excitation light to a surface of a recording medium having aradiation image recorded thereon along a scan line; a light detectionunit which detects signal light emitted from the surface of therecording medium by the scanning of the excitation light within adetection surface intersecting the surface of the recording medium andincluding the scan line; and an optical filter which is disposed betweenthe light detection unit and the surface of the recording medium,wherein each of a transmittance when the excitation light reflected fromthe surface of the recording medium is transmitted through the opticalfilter and a transmittance when the signal light emitted from thesurface of the recording medium at an angle larger than a predeterminedangle with respect to a direction perpendicular to the scan line withinthe detection surface is transmitted through the optical filter issmaller than a transmittance when the signal light emitted from thesurface of the recording medium at an angle smaller than thepredetermined angle with respect to a direction perpendicular to thescan line within the detection surface is transmitted through theoptical filter.
 2. The radiation image reading device according to claim1, wherein when a scan region of the excitation light and a detectionregion of the signal light have a centering alignment relationshipwithin the detection surface, an equation of θ=tan−1 {(W2−W1)/2D} isestablished on the assumption that a width of the scan region isindicated by W1, a width of the detection region is indicated by W2(>W1), a distance between the scan region and the detection region isindicated by D, and the predetermined angle is indicated by θ.
 3. Theradiation image reading device according to claim 1, wherein the opticalfilter includes a glass plate, a first dielectric multilayer film formedon one surface of the glass plate, and a second dielectric multilayerfilm formed on the other surface of the glass plate, and wherein each ofa transmittance when the excitation light reflected from the surface ofthe recording medium is transmitted through the first dielectricmultilayer film and the second dielectric multilayer film and atransmittance when the signal light emitted from the surface of therecording medium at an angle larger than the predetermined angle withrespect to a direction perpendicular to the scan line within thedetection surface is transmitted through the first dielectric multilayerfilm and the second dielectric multilayer film is smaller than atransmittance when the signal light emitted from the surface of therecording medium at an angle smaller than the predetermined angle withrespect to a direction perpendicular to the scan line within thedetection surface is transmitted through the first dielectric multilayerfilm and the second dielectric multilayer film.
 4. The radiation imagereading device according to claim 1, further comprising: an opticalelement which is disposed between the surface of the recording mediumand the optical filter has a function of converges the excitation lightreflected from the surface of the recording medium and the signal lightemitted from the surface of the recording medium only within a surfaceperpendicular to the detection surface.
 5. The radiation image readingdevice according to claim 1, wherein the light detection unit includes aplurality of photodetector elements arranged along a direction parallelto the scan line, and wherein the plurality of photodetector elementsare controlled as one channel.